PVC-FREE SEAL CAP

Abstract

A container closure cap is described comprising a seal consisting of a sealing material, wherein the sealing material is PVC-free, and wherein the sealing material comprises at least one thermoplastic polyurethane elastomer.

Description

PVC-FREE SEAL CAP FIELD OF INVENTION The present invention relates to the field of stoppers commonly used to hermetically seal containers, typically in the context of packaging commercial products, such as food, cosmetics, pharmaceuticals, or others. More particularly, the present invention relates to metal or plastic stoppers adapted to screw on or otherwise apply to, and affix to, the mouth of cups, bottles, vials, or any other glass, metal, or plastic container intended to hold the aforementioned products in a hermetically sealed condition, possibly after having been subjected to a pasteurization and / or sterilization process. BACKGROUND OF THE INVENTION It is known that many commercial products, especially but not exclusively in the food sector, including beverages such as fruit juices, are marketed in cups, glasses, bottles or other glass, metal or plastic containers, which are conventionally equipped with a mouth that, after being filled with the product, is hermetically sealed by means of a corresponding stopper, usually called an "aluminum stopper", which is generally made of metal and / or plastic. These caps can be of multiple types, for example, caps adapted to screw onto the mouth of the container, including “screw caps”, “twist caps”, “handle caps”, “continuous screw caps (CT)”, or caps to be applied to the mouth of the container by pressure or press fit, for example, press twist caps (PT), snap caps and others. To ensure a hermetic seal, all these caps are usually equipped with a seal, typically annular in shape, which can be inseparably attached to the cap and conventionally consists of a polymer-based sealing material. This sealing material, which is generally made up of a composition comprising at least one polymer mixed with other substances, such as lubricants, stabilizers, pigments or other additives, must be able to meet multiple requirements. For example, the sealing material of the seal must be able to be thermally softened sufficiently to be applied to the cap by extrusion and / or other suitable industrial processes, possibly followed or accompanied by mechanical shaping operations intended to give it the desired shape, such as molding, compression molding or injection molding. After application and subsequent cooling, the sealing material of the seal must also assume a solid, more or less deformable and elastic state, capable of maintaining the imposed shape and being able to withstand, on occasion, any heat treatment of pasteurization and / or sterilization, often under overpressure conditions. Especially in the case of screw caps, the sealing material of the seal must also have a coefficient of adhesion to the mouth of the container low enough to allow relatively easy screwing / unscrewing of the cap, preventing the seal from adhering excessively or sticking to the mouth of the container. r mz ίη / ζζηζ / Ε / γίΛΐ At the same time, the sealing material of the seal must guarantee an effective sealing effect throughout the commercial life of the packaged product, acting as a barrier that prevents the infiltration of unwanted substances from the outside and leakage of the product to the outside, for example, of liquid products such as beverages, and which sometimes allows maintaining special internal storage conditions, for example, vacuum and / or controlled atmosphere conditions. To meet all these needs, the seals most conventionally used in the plugs described above consist of a sealing material based on polyvinyl chloride (PVC). However, the current trend in the packaging sector, especially in the food packaging sector, is to eliminate the use of PVC for multiple reasons. One reason is that, during disposal, especially in the case of incineration, PVC releases acidic gases that are pollutants and can be harmful to health. Another reason is that, to manufacture the seals, the PVC-based sealing material generally needs to be supplemented with plasticizers which, under certain conditions, can migrate from the seal into the food product inside the package, with the consequent potential harmful effects on consumers' health. BRIEF DESCRIPTION OF THE INVENTION In light of the foregoing, one objective of the present invention is to make available a closure cap (or aluminum stopper) for containers, which is equipped with a seal that can overcome the drawbacks due to the presence of PVC. Another objective is to achieve the aforementioned purpose in the context of a simple, rational, and relatively cost-effective solution. These objectives are achieved thanks to the features of the invention set forth in independent claim 1. The dependent claims describe preferred and / or particularly advantageous aspects of the invention, but not strictly necessary for its implementation. In particular, one embodiment of the present invention provides a stopper for closing containers comprising a seal comprising a sealing material, wherein - the sealing material is PVC-free, The sealing material comprises at least one thermoplastic polyurethane elastomer. This solution provides a seal that, being PVC-free, preferably completely PVC-free, overcomes all the drawbacks traditionally associated with the use of this polymeric material. On the other hand, the use of a thermoplastic polyurethane elastomer still allows for a seal that has the necessary technical characteristics to meet the requirements demanded in the packaging sector, in particular the ability to guarantee effective sealing, the ability to be easily worked by industrial processes, and the ability not to stick or adhere excessively to the containers. According to one aspect of the invention, the sealing material can have a Shore A hardness between 60 and 95, preferably between 75 and 90. Thanks to these hardness values, it is advantageously possible to obtain a seal that allows for effective sealing on the mouth of the containers, without generating excessive adhesion / sticking phenomena that compromise their opening, and at the same time ensuring good sealing when closed. According to another aspect of the invention, the sealing material can have a density between 1.1 and 1.2 g / cm3 (DIN 53479). This feature is particularly useful in the product packaging phase, even at room temperature, when it is sometimes necessary to guarantee a tight vacuum and prevent leakage of the liquid / preservative even before the heat treatment of pasteurization or sterilization, whereby the seal will then take its final shape, "reproducing" itself on the mouth of the container. Another aspect of the invention provides that the sealing material can have a VICAT softening temperature between 80°C and 90°C (ISO 306). Thanks to this solution, the sealing material can be effectively used to create airtight seals through standard extrusion, thermoforming, compression molding, injection molding, or other suitable industrial processes that require softening the material. According to another aspect of the invention, the seal can be pasteurized up to 100°C; that is, it can be subjected, generally together with the container and the product inside, to a pasteurization process up to 100°C without melting or suffering damage that compromises its integrity and functionality. The seal can also be sterilized up to 125°C and, more preferably, up to 132°C; that is, it can be subjected to a sterilization process up to these temperatures without melting or suffering damage that compromises its integrity and functionality. These aspects of the invention allow the caps equipped with this seal to be used reliably in the packaging of products that require this type of treatment. According to a different aspect of the invention, the thermoplastic polyurethane elastomer can be contained in the sealing material in a weight percentage between 70% and 96% of the total weight of the sealing material (ends included). This amount of thermoplastic polyurethane elastomer allows for a particularly effective and reliable seal. Another aspect of the invention provides that the sealing material may also comprise a second thermoplastic elastomer different from the polyurethane thermoplastic elastomer mentioned above. The addition of this second thermoplastic elastomer, generally in a smaller quantity than polyurethane, can be useful, for example, when a seal is desired with resistance to temperatures above 125°C, and up to 132°C, and / or a seal that is able to withstand back pressures above 4 bar in sterilization cycles. As an example, the second thermoplastic elastomer may be contained in the sealing material at a weight percentage between 5% and 40% of the total weight of the sealing material. This amount of the second thermoplastic elastomer allows maximizing the effects produced by it, without compromising those attributable to the use of the polyurethane thermoplastic elastomer. r mz ίη / ζζηζ / Ε / γίΛΐ Possibly, the sealing material may also comprise one or more additional additives selected from the group consisting of: lubricants, stabilizers, pigments, and fillers. The addition of these substances, generally in quite small quantities or in any case minor quantities with respect to the thermoplastic polyurethane elastomer and the second thermoplastic elastomer (if there is one), has the effect of improving the physical-chemical qualities of the seal. Another aspect of the invention provides that the sealing material can be free of plasticizers, for example, phthalates. The absence of plasticizers, which normally have the drawback of migrating inside some products, especially food products, has the advantage of reducing risks to consumer health. Again, to reduce the risk of product contamination, it is also preferable that the sealing material be free of liquids, i.e., substances that are liquid at room temperature or, in any case, at the temperature of use of the seal (e.g., thinning oils). For the same reasons, the sealing material is also preferably free of any substance that has been identified as harmful to health, including, for example, ADC, OBSH and 2-ethylhexanoic acid. DETAILED DESCRIPTION OF THE INVENTION A stopper according to the present invention can be any stopper adapted to close the mouth of a container. The container can be a cup, a glass, a bottle, a vial, or any other container that is equipped with a mouth, through which a product can be placed into the container and / or can flow out of it. The container can be made of glass, metal, plastic, or any other material that is considered suitable for packaging and storing the product with which it is filled. The product is normally a food product, including beverages such as fruit juices, soft drinks and alcoholic beverages, but it can also be a cosmetic product, a pharmaceutical product or, more generally, any commercial product that must be packaged inside a container or packaging. The stopper, also commonly called an aluminum cap, can be of different types depending on the type of fit achieved with the mouth of the container. For example, the cap may be of the type suitable for fitting onto the container opening by means of a partial or complete thread, which can be obtained at the opening and / or on the cap itself. This allows the cap to be removed later by unscrewing it after filling the container with the product to be packaged and closing the opening. Within this category, the cap may be of the type where the container is sealed by screwing the cap onto the opening, such as screw caps, twist caps, handle caps, or continuous screw caps (CT), or of the type where the seal is achieved by pressure or another means, such as a twist-on cap (PT). In other forms, the cap could be of the types that do not include threading, such as a snap-on cap, hook cap, crimp cap, and others. r tnz ίη / ζζηζ / Ε / γίΛΐ The stopper can be made of metal, plastic, glass, or any other material suitable for the specific application. A seal, typically annular in shape, is generally applied to the cap, the seal of which is adapted to be compressed between the cap and the mouth of the container, in order to act as a barrier that prevents the infiltration of unwanted substances from the outside, and / or leakage of product to the outside, especially if the products are liquid, such as beverages. In some cases, the seal can also act as an airtight seal, and may possibly be able to maintain special internal product preservation conditions, including, for example, vacuum and / or controlled atmosphere conditions. Some applications may also stipulate that the seal must be able to withstand possible sterilization and / or pasteurization treatments of the product that may be carried out after filling and closing the container, which generally involve heating the seal to high temperatures and / or pressures. At these high temperatures and pressures, it is therefore preferable that the seal not melt or be damaged and, ideally, that it maintain its airtight properties. At the same time, the seal should not adhere excessively or stick to the container opening, in order to allow for easy removal of the cap, for example, by unscrewing it, when the container needs to be opened. In order to satisfy these and / or other needs, the seal may consist of a sealing material of a polymeric nature, that is, a material comprising at least one polymeric component, possibly mixed with other substances and additives to form a compound or mixture. The sealing material may be of a type suitable for thermal liquefaction or softening, typically by heating, for example, to give it the shape of the seal, and for solidification to maintain that shape after subsequent cooling. In this way, the sealing material, after softening or becoming sufficiently fluid, can be applied directly to the cap, typically to its inner surface, by means of an extrusion or other similar technological process that can be performed on the area of ​​the cap where the seal is to be made. Once applied to the cap, the sealing material may possibly undergo mechanical shaping, for example, by a compression molding process, in order to give it the shape of the seal to be made. After cooling, the sealing material can therefore assume a solid consistency that allows it to maintain its shape and, after the cap is applied to the container, to perform its sealing function. However, it is not excluded that, in other modalities, the sealing material may be used to make the seal as a separate element outside the cap, for example, by a process of extrusion, injection molding or thermoforming, and then applied as a finished seal to the cap, for example, inserted within a special seat obtained therein. In this case as well, the sealing material must in all cases be capable of softening or becoming sufficiently fluid, after appropriate heating, to undergo the aforementioned forming processes, and solidify, retaining the acquired shape, after subsequent cooling. According to an important aspect of the present invention, the sealing material constituting the seal is free of polyvinyl chloride (PVC). It is wish to specify here that, in the context of this discussion, when it is said that the sealing material is free of a substance, (for example, PVC), it means that the sealing material is completely free of that substance, i.e., there is no trace of that substance in it, or at most the substance in question is present in an amount by weight less than or equal to 1% of the total weight of the sealing material, preferably less than 0.5% of the total weight of the sealing material and, even more preferably, less than 0.1% of the total weight of the sealing material. In contrast, the sealing material comprises at least firstly a thermoplastic polyurethane elastomer (or elastic polymer). This thermoplastic polyurethane elastomer may be contained in the sealing material at a weight percentage between 70% and 96% of the total weight of the sealing material (ends included). The thermoplastic polyurethane elastomer can be obtained by combining, for example, through polyaddition, a polyfunctional isocyanate, for example, a diisocyanate, with one or more polyols (or long-chain diols) and, eventually, with other additives, such as one or more short-chain diols and / or chain extenders. A polyfunctional isocyanate is generally an organic substance whose molecule contains two or more isocyanate groups (-NCO). An organic substance whose molecule contains two isocyanate groups is conventionally called a diisocyanate. The polyfunctional isocyanate, for example, diisocyanate, can be aliphatic, cycloaliphatic, polycyclic, or aromatic. In particular, the polyfunctional isocyanate may be a diisocyanate selected from the group consisting of: diphenylmethane diisocyanate (MDI), toluene diisocyanate (TDI), and xylene diisocyanate (XDI). Each of the polyols present in the thermoplastic elastomer can be selected from the group consisting of: a polyether, a polyester, and a polycaprolactone. In some embodiments, the sealing material that constitutes the seal may also comprise a second thermoplastic elastomer (or elastic thermoplastic polymer), which is different from the first thermoplastic polyurethane elastomer. For example, the second thermoplastic elastomer can be of the styrene type (SBS; SEBS), or simply a polyolefin resin, (e.g. polyethylene, polypropylene, polybutene). When it is necessary to have a greater elastic nature of the finished seal, especially if it is subjected to temperatures above 125°C and back pressures in a closed environment above 4 bar, then a styrene thermoplastic elastomer will increase the necessary mechanical characteristics, for example, thanks to its glass transition properties of -90°C (i.e., 90° below zero), Shore hardness equal to 13 A and a density between 0.89 and 1.20 g / cm3. The second thermoplastic elastomer may be contained in the sealing material in a percentage by weight between 5% and 40% of the total weight of the sealing material, for example, between 5% and 25%. The sealing material may optionally also include other additives selected from the group consisting of: lubricants, stabilizers, pigments and fillers. Lubricants are used to reduce the adhesion of the seal to the material that makes up the mouth of the container, so as to facilitate its opening and closing, and can be selected, for example, from the group consisting of micronized amide and polyethylene waxes. Stabilizers are used to stabilize the material against temperature and UV degradation and oxidation and can be selected, for example, from the group consisting of Ca and Zn salts. The pigments are used to give the seal a predetermined color and can be selected, for example, from the group consisting of titanium dioxide. Each of these additives may be present in the sealing material in proportions by weight less than the first thermoplastic polyurethane elastomer and the second thermoplastic elastomer (if any), for example, less than or equal to 5% of the total weight of the sealing material, and preferably less than or equal to 1% of the total weight of the sealing material. Since the seal may come into contact with the product packaged in the container, which may be food-related, it is also preferable that the sealing material be free of all substances that, by contaminating and / or migrating into the product, could be hazardous to health. Thus, for example, it is preferable that the sealing material be free of plasticizers, such as phthalates and adipates. It is also preferable that the sealing material be free of liquids, that is, of substances that are liquid at room temperature or, in any case, at the normal operating temperature of the seal, for example, plasticizers of any nature, whether polar or non-polar, and of any molecular weight, and in general of liposoluble diluent oils. For the same reasons, the sealing material is preferably free of substances including, for example, ADC, OBSH, 2-ethylhexanoic acid. Regardless of these considerations, it is preferable that the composition and / or manufacturing methods of the sealing material be selected in such a way that, after solidification into a seal, it has one or more of the following physical characteristics: - Shore A hardness between 60 and 95 (inclusive), more preferably between 75 and 90 (inclusive); - density between 1.1 and 1.2 g / cm3 (DIN 53479) (ends included); - VICAT softening temperature between 80°C and 90°C (ISO 306) (inclusive ends). It is also preferable that the seal obtained with said sealing material can withstand the sterilization and / or pasteurization processes to which the product may be subjected inside the container after the cap is closed. The term “resist” means that the seal, when subjected to these processes, must not melt, break, be damaged or lose its effectiveness. In particular, it is preferable that the seal can withstand sterilization processes that involve heating it to a temperature of 100°C (including the end). r tnz ίη / ζζηζ / Ε / γίΛΐ It is also preferable that the seal can withstand pasteurization processes involving heating it to a temperature of 125°C (inclusive end) and, more preferably, to a temperature of 132°C (inclusive end). In the case of pasteurization, it is also possible that this process is carried out in a pressurized environment, in which case the seal should preferably be able to withstand the action of pressure, without compromising the airtight closure of the container. Notwithstanding the foregoing, a first embodiment of the present invention provides that the sealing material of the joint comprises a single polymer, and that this polymer is the aforementioned thermoplastic polyurethane elastomer. In this case, the composition of the sealing material can be the following: - a thermoplastic polyurethane elastomer; - optionally at least one lubricant; - optionally at least one stabilizer; - optionally at least one pigment; - optionally at least one filling. As an example, a concrete example of this sealing material could be the following: - Thermoplastic polyurethane (ether or ester base) (> 90%) - Fatty acid ester (<5%) - Titanium dioxide (<5%) A second embodiment of the present invention provides that the sealing material of the seal comprises two or more different polymers, and that these polymers include the first thermoplastic polyurethane elastomer mentioned above and the second thermoplastic elastomer mentioned above. In this case, the composition of the sealing material can be the following: - a thermoplastic polyurethane elastomer; - at least a second thermoplastic elastomer different from said thermoplastic polyurethane elastomer; - optionally at least one lubricant; - optionally at least one stabilizer; - optionally at least one pigment; - optionally at least one filling. As an example, a concrete example of this sealing material could be the following: - Thermoplastic polyurethane (ether or ester based) (>50% and <90%) - SEBS olefin copolymer (>10% and <40%) - Polyolefin elastomer (>10% and <40%) - fatty acid ester (<5%) - titanium dioxide (<5%) However, all these modalities are united by the fact that the sealing material is PVC-free and, preferably, also free of polyolefins and / or plasticizers and / or liquids and / or ADC and / or OBSH and / or 2-ethylhexanoic acid. r mz ίη / ζζηζ / Ε / γίΛΐ In all embodiments, the quantities of the individual components may naturally vary depending on the specific intended use, but preferably remain within the ranges mentioned above. Clearly, a skilled tradesperson may make numerous technical and application modifications to everything described above without departing from the scope of the invention as claimed below.

Claims

1. A metal stopper for closing containers comprising a seal made of a sealing material, characterized in that: - the sealing material is PVC-free, i.e., PVC is completely absent from the sealing material, - the sealing material comprises at least one thermoplastic polyurethane elastomer, and a second thermoplastic elastomer different from the thermoplastic polyurethane elastomer, said second thermoplastic elastomer being a styrene-type thermoplastic elastomer, the sealing material is liquid-free, i.e., liquids are completely absent from the sealing material.

2. The plug according to claim 1, further characterized in that the sealing material has a Shore A hardness between 60 and 95, inclusive of the ends.

3. The plug in accordance with any of the preceding claims, further characterized in that the sealing material has a density, measured according to DIN 53479, between 1.1 and 1.2 g / cm3, inclusive of the ends.

4. The plug in accordance with any of the preceding claims, further characterized in that the sealing material has a VICAT softening temperature, measured according to ISO 306, between 80°C and 90°C, inclusive of the ends.

5. The stopper in accordance with any of the preceding claims, further characterized in that the seal can be pasteurized up to temperatures equal to 100°C.

6. The stopper in accordance with any of the preceding claims, further characterized in that the seal can be sterilized up to temperatures equal to 132°C.

7. The plug according to any of the preceding claims, further characterized in that said thermoplastic polyurethane elastomer is contained in the sealing material in a weight percentage between 70% and 96% of the total weight of the sealing material, including the ends.

8. The cap according to claim 1, further characterized in that the second thermoplastic elastomer is contained in the sealing material in a weight percentage between 5% and 40% of the total weight of the sealing material.

9. The plug in accordance with any of the preceding claims, further characterized in that the sealing material comprises one or more additives selected from the group consisting of: lubricants, stabilizers, pigments and fillers.

10. The cap in accordance with any of the preceding claims, further characterized in that the sealing material is free of plasticizers, i.e., the plasticizers are completely absent from the sealing material.